1. Field of the Invention
The present invention relates to a control circuit for automobile headlamps, such as fog lamps, which emit light in variable color. The control circuit prevents left and right headlamps from emitting beams of light in different colors.
2. Related Background Art
It has hitherto been in practice to use a headlamp emitting a beam of yellow-colored light or a headlamp emitting a beam of white-colored light for an automobile. However, recently a lamp which permits a selection of a desired color for a beam of the emitted light as freely selected from a list of available colors, such as a white color and a yellow color is used. FIG. 9 is a diagram which illustrates the construction of a device capable of controlling a selection of a color for the light emitted from a headlamp. In FIG. 9, the revolution of a motor 80 is transmitted to a worm wheel 87 via a worm gear 81, and a pinion gear 82, which forms a structure unified with the worm wheel 87 and rotates together with the worm wheel 87 in one block.
This revolution of the worm wheel 87 places a rack 83, which is in its engagement with the pinion gear 82, into its straight-line motion. Then, a yellow globe 84, which is set in the upper part of the rack 83, moves forward or backward as one structure with the rack 83. This movement causes the yellow globe 84 to approach a bulb 85 or to move away from it, so that yellow globe 84 covers the bulb 85 when the yellow globe 84 has approached a point nearest to the bulb 85, and a beam of yellow light is therefore emitted. On the other hand, when the yellow globe 84 has moved farthest away from the bulb 85, the light emitted from the bulb 85 is reflected by a reflecting mirror 86 and is projected as a beam of white light.
In this manner, the driving force derived from the motor 80 can be applied so as to make the color of the light emitted from the headlamp either white or yellow.
However, such a prior art device as the one described above is not capable of controlling the color of the light when a fault has occurred in the motor or another part of its driving system because the yellow globe will stop at the location where it presently is when such a trouble occurs. On the other hand, since there are two headlamps, a left lamp and a right lamp, in a system, which performs color control by a synchronized operation, if the driving system for one of the two lamps has a fault, it is not possible for the system to perform any synchronized operation. Accordingly, the left and right headlamps will respectively emit beams of light of a different color, which presents a disadvantage in that it is in itself an undesirable condition from the viewpoint of safety in driving. This is so, because the beams of light projected ahead of the motor vehicle are different in color between the left headlamp and the right headlamp, such a difference in the color of the light beams producing a difference in the visual perception of the distance from objects which the beams of light are projected onto.